style: apply ruff format across backend + scripts (line-length 100)

Mechanical, whole-tree `ruff format` pass — no behaviour change. Recorded in
.git-blame-ignore-revs (next commit) so git blame skips it.

backend/app/ratelimit.py

@@ -6,6 +6,7 @@ is fine for abuse throttling (not for anything that must survive a deploy). Not
 processes — if we ever run multiple workers, swap the backing store for Redis behind the same
 ``allow()`` interface.
 """
+
 import threading
 import time